Russia’s decision to lift a self-imposed ban on supplying an advanced air defense system to Iran is reverberating in Washington, where officials worry the move could lead to a series of complications, some of which could further destabilize the Middle East.

Some of the harshest criticism came from the State Department, which said Secretary of State John Kerry had voiced Washington’s concerns directly to Russian Foreign Minister Sergei Lavrov.

"We think given Iran's destabilizing actions in the region, in places like Yemen or Syria or Lebanon, that this isn't the time to be selling these kinds of systems to them," State Department spokeswoman Marie Harf said.

Earlier Monday, the Kremlin's website reported Putin had signed a decree lifting a ban on providing Iran with the S-300 system. The announcement Monday comes as world powers are trying to negotiate a final nuclear deal with Iran, aimed at curtailing Tehran’s nuclear program to ensure it does not develop nuclear weapons.

Moscow signed a contract worth $800 million back in 2007 to supply Tehran with five S-300 batteries. However, Russia froze the contract three years later after the United Nations Security Council imposed sanctions on Iran.

The S-300 surface-to-air missile system is not Russia’s most advanced, but it's capable of simultaneously hitting multiple targets, like incoming missiles and aircraft, simultaneously, even at high altitude. It boasts a range of up to 200 kilometers, expansive enough that some analysts suggest it could be used for more than defensive purposes.

Harf said that the transfer of S-300 missiles to Iran would not violate existing U.N. Security Council sanctions, but that the U.S. believes the timing is poor.

She downplayed concerns that Russia’s move to clear the way for the sale of the S-300 system will scuttle a nuclear deal between Iran and six world powers. The United States and Russia "have been in lockstep inside the negotiating room in these negotiations," she said.

The other four world powers among the so-called P5+1 nations are China, France, the United Kingdom and Germany.

Lavrov: No more rationale for ban

Lavrov, explaining the decision to lift the S-300 ban, said that with the recent framework deal the rationale for the international embargo and Russia's own ban had "completely disappeared."

Lavrov added that the S-300 is "exclusively defensive in nature, not adapted for offensive purposes and will not jeopardize the security of any state in the region, including, of course, Israel."

Meanwhile, Israeli Intelligence Minister Yuval Steinitz said Monday that Russia's lifting of the S-300 ban was a "direct result" of the "legitimacy" Iran is receiving from the framework nuclear deal, and proof that Iran will use the lifting of sanctions to arm itself rather than improve its people's living conditions.

Others express concerns

Delivery of the air defense system could affect leverage in the negotiations and even options for Western nations if a deal falls through, some analysts also contend.

"The Iranians desperately want a new long-range [surface-to-air missile] system to form the centerpiece of an integrated air defense network that will deter anyone who might want to enter its airspace,” said Jeremy Binnie, Middle East editor ofIHS Jane's Defence Weekly. "I think it would be fair to say it [the S-300] would complicate a strike against Iran's nuclear infrastructure."

Brian Katulis at the Center for American Progress believes the potential fallout could be even more widespread in a region where old rivalries, like those between Iran and Saudi Arabia, already are inflamed and playing out in places like Yemen. There, a Saudi-led coalition is carrying out airstrikes against the Iranian-backed Houthi rebels.

"I look for every action like that to have a reaction so the Gulf countries, Saudi Arabia, the [United Arab Emirates], Bahrain, others, Qatar, doing reaction to that," Katulis said.

A U.S. military official said the S-300 would be a significant upgrade, describing it as a "very capable system," but thinks it is unlikely the advanced system ever would end up in the hands of Tehran’s regional proxies.

"A high-end system like this would be used specifically for Iran," the official said.

Barter agreement

Also Monday, Russian Deputy Foreign Minister Sergei Ryabkov said Moscow is supplying Iran with grain, equipment and building materials under an ongoing, "very significant" barter agreement.

White House spokesman Josh Earnest said proposals "to essentially barter Iranian oil for Russian goods" are being discussed but haven't been implemented. He said such a deal could raise "serious concerns" by interfering with the sanctions imposed on Iran by the United States and other Western nations.

Sources told the Reuters news agency more than a year ago that a deal worth up to $20 billion was being discussed with Tehran and would involve Russia buying up to 500,000 barrels of Iranian oil a day in exchange for Russian equipment and goods.​

Ryabkov suggested Russia had high hopes that its steadfast support for Iran would pay off in energy cooperation once international sanctions against the Islamic republic are lifted.

He also reiterated Moscow's line that an arms embargo on Iran should be lifted once a final nuclear deal is sealed.

One upper-house lawmaker asked Ryabkov whether lifting sanctions on Tehran could undermine Russia's position on global energy markets, including as the main gas supplier to Europe.

"I am not confident as yet that the Iranian side would be ready to carry out supplies of natural gas from its fields quickly and in large quantities to Europe," Reuters quoted him as saying. "This requires infrastructure that is difficult to build."